Unequivocal characterisation of a [Ln(terpy)(NO3)3 �/(H2O)] complex.The synthesis and structure of [M(terpy)(NO3)3 �/(H2O)] (M�/Eu, Tb);

a comparison with the structure of [Eu(bipy)2(NO3)3]and with other europium nitrate complexes

{terpy�/2,2?:6?,2ƒ-terpyridyl; bipy�/2,2?-bipyridyl}

Simon A. Cotton a,*, Oliver E. Noy a, Florian Liesener b, Paul R. Raithby b,*a Uppingham School, Uppingham, Rutland LE15 9QE, UK

b Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK

Received 10 May 2002; accepted 13 August 2002

Abstract

The complexes [M(terpy)(NO3)3 �/(H2O)] (M�/Eu (1), Tb(2); terpy�/2,2?:6?,2ƒ-terpyridyl) are isomorphous and crystallise in the

triclinic space group P1 with Z�/2, while the related complex [Eu(bipy)2(NO3)3] (3) (bipy�/2,2?-bipyridyl) crystallises in the

orthorhombic space group Pcan (non-standard setting of Pbcn ) with Z�/4 such that the two halves of the molecule are related by a

crystallographic twofold axis. In each of the three complexes the metal atom is 10 co-ordinate and all three contain three bidentate

nitrate groups. In complexes 1 and 2 the coordination sphere is completed by the three nitrogen donor atoms of the terpyridine

ligand and by the oxygen donor atom of the coordinated water solvent molecule. In complex 3 the coordination sphere is completed

by two nitrogen donor atoms from each of the two bipyridine ligands. These structures are compared with other lanthanide

complexes of related ligands and the factors affecting the co-ordination geometry evaluated.

# 2002 Elsevier Science B.V. All rights reserved.

Keywords: Europium; Terbium; Nitrate; 2,2?:6?,2ƒ-Terpyridyl; 2,2?-Bipyridyl; X-ray structures

1. Introduction

Complexes of the 2,2?:6?,2ƒ-terpyridine ligand (terpy)

are attracting considerable interest. The ruthenium and

osmium complexes have photochemical potential [1]

and, in addition to their luminescent properties, plati-

num complexes show specific interaction with nucleic

acids [2]. Lanthanide complexes are models for studying

the separation of lanthanides and actinides from radio-

active waste [3].

The co-ordination chemistry of the lanthanides is

dominated by O-donor ligands [4,5] as expected for

oxophilic metal ions [6]. N-donors form stable com-

plexes in non-aqueous solvents; most studies have

centred upon the bidentate ligands 2,2?-bipyridyl and

1,10-phenanthroline. Although first reported by Sinha

in 1965, the structure of 1:1 complexes of terpyridyl with

lanthanide nitrates is still unclear, hydrated species

[Ln(terpy)(NO3)3 �/(H2O)n ] having several times been

proposed without definite confirmation. Complexes

formulated as [Ln(terpy)(NO3)3 �/nH2O] (Ln�/Tb, n�/

0; Ln�/Tm, Yb, n�/1; Ln�/Dy, Ho, n�/2; Ln�/Er;

n�/3) were described in the initial publication [7]. Only

recently has further evidence been obtained, in the form

of NMR spectra [8] assigned to [La(terpy)(NO3)3 �/H2O]

and reports [9] of [Ln(terpy)(NO3)3 �/H2O] (Ln�/La, Pr,

Er, Yb) and [Ln(terpy)(NO3)3] (Ln�/Gd, Yb), which,

however, lacked structural confirmation. Semenova and

White have found that the earlier members of the

lanthanide series form [Ln(terpy)(NO3)2(H2O)3][NO3]

* Corresponding authors. Present address: Department of

Chemistry, University of Bath, Claverton Down, Bath BA2 7AY,

UK (P.R.R.). Tel.: �/44-1225-323 183; fax: �/44-1225-826 231.

E-mail addresses: sac@uppingham.co.uk (S.A. Cotton),

p.r.raithby@bath.ac.uk (P.R. Raithby).

Inorganica Chimica Acta 344 (2003) 37�/42

www.elsevier.com/locate/ica

0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 2 6 6 - 5

(Ln�/La�/Gd) and the later lanthanides form

[Ln(terpy)(NO3)2(H2O)2][NO3] �/2H2O (Ln�/Tb, Lu, Y)

on crystallisation from MeCN then water [10]. The

structure of [Gd(terpy)(NO3)2(H2O)3][NO3] has alsobeen reported independently [3]. In a recent compre-

hensive structural study of lanthanide terpyridine nitrate

complexes Drew et al. have identified no less than five

different structural types the formation of which

appears to depend upon the size of the particular

lanthanide ion and upon the conditions used for crystal-

lisation [11]. In type I complexes, structurally charac-

terised for [Nd(terpy)(NO3)3 �/H2O], the metal is 10 co-ordinate, being bonded to the terdentate terpy ligand,

three bidentate nitrates and a water molecule. The type

II complexes are salts with the general formula [M(ter-

py)2(NO3)2][M(terpy)(NO3)4] (M�/Nd, Sm, Tb, Dy,

Ho). The metal in the cation is 10 co-ordinate, and is

bonded to two terdentate terpy ligands and two

bidentate nitrate groups. The metal in the anion is also

10 co-ordinate, being linked to one terdentate terpyligand, and three bidentate and one unidentate nitrate

group. In type III complexes a free terpy ligand that is

hydrogen bonded to a co-ordinated water molecule is

found in the crystal structures of the Ho, Er, Tm and Yb

complexes that have the general formula

[M(terpy)(NO3)3 �/H2O] �/(terpy). Here the lanthanide

ion has a similar co-ordination geometry to that

observed in the type I system. In type IV complexes,characterised for [Tm(terpy)(NO3)3 �/H2O], the metal is

only nine co-ordinate being bonded to the terdentate

terpy ligand, two bidentate nitrates, one unidentate

nitrate, and a water molecule. In type V complexes,

structurally characterised for [Yb(terpy)(NO3)3], the

metal is again nine co-ordinate, being bonded to a

terdentate terpy ligand and three bidentate nitrates

groups.In our study [12] of the effect of changes in solvent

and lanthanide ion upon the composition and geometry

of these 1:1 complexes, we have already reported the

synthesis and structure of the erbium complex

[Er(terpy)(NO3)3 �/(C2H5OH)], which has a structure

related to that of the type IV complexes described

above, and features two bidentate and one monodentate

nitrate groups as well as a coordinated ethanol molecule.In this paper we establish that the structural type I is not

restricted to the early lanthanide elements, and report

the structures of the [Ln(terpy)(NO3)3 �/(H2O)] (M�/Eu

(1), Tb(2)) complexes, together with the structure of

[Eu(bipy)2(NO3)3] (3) which also contains three biden-

tate nitrate groups.

2. Experimental

All reagents and solvents were used as purchased

(Aldrich) without further purification.

2.1. Preparation of the lanthanide complexes

Reaction of [Eu(NO3)3 �/6H2O] with terpy in a 1:1

ratio in EtOH afforded colourless crystals of[Eu(terpy)(NO3)3 �/(H2O)] (1) that were recrystallised

from MeCN to give crystals that proved suitable for

X-ray diffraction study. Colourless crystals of

[Tb(terpy)(NO3)3 �/(H2O)] (2) were obtained directly

from the reaction of hydrated terbium nitrate with terpy

in EtOH. The complex [Eu(bipy)2(NO3)3] (3) was

prepared as colourless crystals from the reaction of

[Eu(NO3)3 �/6H2O] with bipy in a 1:2 ratio in EtOH bythe general method of Hart and Laming [13]. Micro-

analytical results obtained for all these compounds were

misleading and may reflect loss of solvent on standing.

Similarly variable results have been noted previously by

Sinha [7]. Our crystallographic results give us confidence

in the composition of these compounds.

2.2. X-ray crystallography

The crystal data, data collection parameters, and

structure solution and refinement details for the three

structures determined are presented in Table 1. Datacollection was carried out on a Stoe 4-circle diffract-

ometer, for 1, and a Rigaku AFC7 diffractometer, for 3,

both equipped with graphite monochromated Mo Karadiation and an Oxford Cryostream cooling apparatus.

The structure of 2 was determined at room temperature

on a Rigaku R-AXIS II imaging plate diffractometer. In

Table 1

Selected crystal data and structure solution and refinement parameters

for complexes 1, 2 and 3

1 2 3

Empirical formula C15H13Eu-

N6O10

C15H13N6-

O10Tb

C20H16EuN7O9

Formula weight 589.27 596.23 650.36

Temperature (K) 166(2) 290(2) 180(2)

Crystal system triclinic triclinic orthorhombic

Space group /P1/ /P1/ Pcan

a (A) 8.224(6) 8.354(5) 9.037(2)

b (A) 10.846(8) 10.837(5) 16.782(2)

c (A) 10.958(8) 11.049(5) 15.014(5)

a (8) 94.29(6) 94.07(3) 90

b (8) 93.58(6) 93.83(3) 90

g (8) 101.74(6) 102.13(3) 90

V (A3) 951.3(12) 972.1(9) 2277(1)

m (mm�1) 3.369 3.708 2.823

Reflections collected 3847 6052 5861

Independent reflections 3343 3364 2003

Rint 0.0337 0.0413 0.121

Parameters 295 296 169

R1 (observed data) 0.0253 0.0325 0.0375

wR2 (all data) 0.0663 0.0699 0.1065

S.A. Cotton et al. / Inorganica Chimica Acta 344 (2003) 37�/4238

each case the data was corrected for Lp effects and for

absorption (using a semi-empirical method based on psi-

scans for 1 and 3, and using interframe scaling for 2).

Structure solution was achieved by Patterson methods(SHELXS-86 [14]) and refined by full-matrix least-squares

on F2 (SHELXL-97 [15]) with all non-hydrogen atoms

assigned anisotropic displacement parameters. Hydro-

gen atoms attached to carbon atoms were placed in

idealised positions and allowed to ride on the relevant

carbon atom. The hydrogen atoms of the co-ordinated

water molecule for structures 1 and 2 were located from

Fourier difference maps and refined with additionalrestraints O�/H distances fixed at 0.96 A. In the final

cycles of refinement a weighting scheme that gave a

relatively flat analysis of variance was introduced and

refinement continued until convergence was reached.

3. Results and discussion

3.1. Crystal structure of [Eu(bipy)2(NO3)3] (3)

The complex [Eu(bipy)2(NO3)3] crystallises in the

orthorhombic space group Pcan (non-standard setting

of Pbcn) and is isomorphous and isostructural with the

[Ln(bipy)2(NO3)3] (Ln�/La, Nd, Pr and Lu) analogues

[16,17]. The crystal structure contains isolated

[Eu(N ,N ?-bipy)2(O ,O ?�/NO3)3] complexes (Fig. 1). The

co-ordination number of the europium atom in thecomplex is 10. The molecule sits on a twofold axis that

passes through the N(4) and O(5) atoms of one of the

nitrate groups and the europium atom Eu(1). Selected

bond parameters for 3 are listed in Table 2. The

coordination polyhedron in these compounds has been

variously described as a bicapped dodecahedron or as a

sphenocorona [16]. There are no particularly short

hydrogen bonds in the crystal structure, presumably

because good hydrogen bond donors are absent. Neither

is there any evidence for the presence of graphitic

packing between the bipy groups. The most significant

intermolecular interactions are C�/H� � �O hydrogen

bonds; C(4)�/H(4a)� � �O(1), H(4a)� � �O(1) 2.624 A,

C(4)�/H(4a)� � �O(1) 174.648 [where O(1) is related by

the symmetry operation x�/0.5, 1.5�/y , z ]; C(2)�/

H(2a)� � �O(3), H(2a)� � �O(3) 2.473 A, C(2)�/

H(2a)� � �O(3) 139.968 [where O(3) is related by the

symmetry operation 2.5�/x , 1.5�/y , 0.5�/z ]. The aver-

age Eu�/N bond length of 2.547 A and Eu�/O distance of

2.515 A can be compared with the respective values of

2.625 and 2.570 A in the praseodymium analogue [17]; a

difference of approximately 0.06 A would be predicted

from ionic radius considerations [18]. The O�/Eu�/O

nitrate bite angle of 50.7(9)8 falls close to the values of

48.0(3) and 50.5(3)8 found in the lanthanum and

lutetium analogues, respectively [16]. Similarly, the N�/

Eu�/N bipyridine bite angle of 63.4(2)8 falls between the

values of 60.1(3) and 66.5(4)8 reported for the lantha-

num and lutetium compounds, respectively. The bond

parameters within the bipy and nitrate ligands fall

within the expected range [16,17] and the dihedral angle

between the two rings of the unique bipy ligand is

12.128. This twist reduces unfavourable steric interac-

tions between the protons on the adjacent rings. The

nitrate groups are effectively planar, the group

N(4)O(4)O(4a)O(5) by symmetry, and the dhedral angle

between the two unique groups is 63.758.In the 10 co-ordinate [Eu(NO3)5]2� ion (studied as

the [Ph4As]� salt [19]), the average Eu�/O distance is

2.481 A, indicating a lack of congestion and concomi-

tant short Eu�/O distances due to the small bite angle of

the nitrate ion, an effect also noted in a study of

praseodymium complexes of bipy [17]. Comparison

with 10 co-ordinate complexes of monodentate ligands

[20] of the type [EuL4(NO3)3] (L�/H2O, Me2SO) in

[Eu(H2O)4(NO3)3] �/H2O and [Eu(Me2SO)4(NO3)3] is

also instructive, with average Eu�/O distances of 2.54

and 2.61 A, respectively, indicating the greater steric

demand of monodentate ligands in complexes with the

Fig. 1. The molecular structure of [Eu(bipy)2(NO3)3] (3) showing the

atom numbering scheme. Ellipsoids are set at a value of 30%. The

molecule sits on a crystallographic twofold axis that passes through

Eu(1), N(4) and O(5). The two halves of the molecule are related by the

symmetry operation x , �/y�/2, �/z�/3/2.

Table 2

Selected bond lengths (A) and angles (8) for [Eu(bipy)2(NO3)3] (3)

Bond lengths

Eu(1)�/N(1) 2.554(5) Eu(1)�/N(2) 2.540(5)

Eu(1)�/O(1) 2.494(4) Eu(1)�/O(2) 2.561(5)

Eu(1)�/O(4) 2.491(5)

Bond angles

O(2)�/N(3)�/O(1) 116.5(5) O(3)�/N(3)�/O(1) 121.6(5)

O(3)�/N(3)�/O(2) 121.9(5) O(5)�/N(4)�/O(4) 121.7(4)

O(4)�/N(4)�/O(4A) 116.6(7)

The atom denoted O(4A) is related to O(4) by the symmetry

operation x , �/y�/2, �/z , �/3/2.

S.A. Cotton et al. / Inorganica Chimica Acta 344 (2003) 37�/42 39

same coordination number. The relatively short average

Eu�/O distance of 2.47 A in the 10 co-ordinate [Eu(12-

crown-4)(NO3)3] is in accord with this view [21].

In the 11 co-ordinate [Eu(15-crown-5)(NO3)3], whichagain has three bidentate nitrates, the average Eu�/O

(nitrate) distance is 2.53 (8) A, with one particularly long

bond of 2.65 A, consistent with increased steric crowd-

ing around the metal centre [22].

3.2. Crystal structure of [Eu(terpy)(NO3)3 �/(H2O)]

(1)

The complex 1 crystallises in the triclinic space group

P1 and the asymmetric unit of the cell contains an

independent molecule of [Eu(terpy)(NO3)3 �/(H2O)]. The

molecular structure is shown in Fig. 2 while selected

bond parameters are listed in Table 3. With the presenceof the co-ordinated water molecule in this complex both

strong hydrogen bond donors and acceptors are present

and, as a consequence, hydrogen bonded interactions

play a more important role than in the case of the bipy

complex 3. The water forms intermolecular hydrogen

bonds, acting as a donor to nitrate oxygen atoms

[O(10)� � �O(5), 2.932 A; H(10a)� � �O(5), 2.040 A;

O(10)�/H(10a)� � �O(5), 170.878; with O(5) related bythe symmetry operation �/x , �/y , �/z ; and

O(10)� � �O(3), 2.936 A; H(10b)� � �O(3), 2.051 A, O(10)�/

H(10b)� � �O(3), 167.098; with O(3) related by the sym-

metry operation �/x , �/y , 1�/z ]. These interactions

result in a hydrogen bonding network forming puckered

sheets approximately parallel to the bc plane. In

addition, there are weak C�/H� � �O�/NO2 intermolecular

interactions between the hydrogen atoms of the terpyligand and the nitrate oxygen atoms [H(3a)� � �O(1),

2.606 A, C(3)�/H(3a)� � �O(1) 107.78; where O(1) is

related by the symmetry operation x�/1, y , z ;

H(8a)� � �O(6), 2.694 A, C(8)�/H(8a)� � �O(6), 108.88;where O(6) is related by the symmetry operation 1�/

x , 1�/y , �/z , and H(14a)� � �O(7), 2.468 A, C(14)�/

H(14a)� � �O(7), 121.48; where O(7) is related by the

symmetry operation x�/1, y , z ]. Similar C�/H� � �O inter-

actions have been reported for [Er(terpy)(NO3)3 �/(C2H5OH)] [12] previously. There is also evidence for

the presence of graphitic packing between the rings of

the terpy ligands on adjacent molecules. The shortest

ring centroid to ring centroid contact, of 3.607 A,

between the central ring {N(2)C(6)C(7)C(8)C(9)C(10)}

of one molecule and one of the outer rings

{N(1)C(1)C(2)C(3)C(4)C(5)} of a molecule related by

the symmetry operation 1�/x , 1�/y , 1�/z . The other

ring� � �ring distances are in excess of 4 A.

In 1 the europium atom is again 10 co-ordinate. The

average Eu�/N bond length of 2.554 A and the average

Eu�/O distance of 2.517 A are in very close accord with

the values of 2.547 and 2.515 A, respectively for the bipy

analogue (vide supra). In comparison with [Eu(bi-

py)2(NO3)3] (3), a coordination number of 10 has been

maintained by substitution of one terpyridyl molecule

and a water molecule for the two bipy ligands but the

terpy ligand enforces pseudo -meridional binding to the

lanthanide, dictating positions for the remaining li-

gands. The oxygen atom of the water molecule is

effectively coplanar with the nitrogen atoms of the terpy

ligand. Within the terpy ligand the N(1)�/C(5) ring

makes dihedral angles of 8.048 with the N(2)�/C(10)

ring, and 12.838 with the N(3)�/C(15) ring. The dihedral

angle between the N(2)�/C(10) and N(3)�/C(15) rings is

Fig. 2. The molecular structure of [Eu(terpy)(NO3)3 �/(H2O)] (1)

showing the atom numbering scheme adopted. Ellipsoids are set at a

value of 30%.

Table 3

Selected bond lengths (A) and angles (8) for [M(terpy)(NO3)3 �/(H2O)]

(M�/Eu (1), Tb(2))

Eu (1) Tb (2)

Bond lengths

Ln(1)�/N(1) 2.538(4) 2.539(4)

Ln(1)�/N(2) 2.550(4) 2.546(4)

Ln(1)�/N(3) 2.574(4) 2.564(4)

Ln(1)�/O(1) 2.494(4) 2.489(4)

Ln(1)�/O(2) 2.582(4) 2.586(4)

Ln(1)�/O(4) 2.533(3) 2.529(4)

Ln(1)�/O(5) 2.503(4) 2.482(4)

Ln(1)�/O(7) 2.486(4) 2.482(5)

Ln(1)�/O(8) 2.502(4) 2.491(5)

Ln(1)�/O(10) 2.408(4) 2.394(4)

Bond angles

O(2)�/N(4)�/O(1) 116.4(4) 116.3(4)

O(3)�/N(4)�/O(1) 120.8(4) 119.4(6)

O(3)�/N(4)�/O(2) 122.8(4) 124.3(5)

O(5)�/N(5)�/O(4) 116.8(3) 116.4(4)

O(6)�/N(5)�/O(4) 122.7(4) 122.7(4)

O(6)�/N(5)�/O(5) 120.5(4) 120.9(5)

O(8)�/N(6)�/O(7) 115.1(4) 115.1(5)

O(9)�/N(6)�/O(7) 122.5(5) 122.7(6)

O(9)�/N(6)�/O(8) 122.4(4) 122.1(6)

S.A. Cotton et al. / Inorganica Chimica Acta 344 (2003) 37�/4240

12.408. The three nitrate groups are essentially planar.

The ‘equatorial’ nitrate group, N(6), O(7), O(8), O(9),

makes a dihedral angle of 51.998 with the central terpy

ring, N(2)�/C(10).

Eu�/N bonds to co-ordinated terpyridyl molecules

average 2.575 A in the nine co-ordinate [Eu(ter-

py)3](ClO4)3 [23] and lie in the range 2.542�/2.551 A in

[Eu(terpy)Cl(H2O)n ]Cl2 �/3H2O (n�/4�/5) [24]. The Eu�/

N distances in the 10 co-ordinate

2,2?:6?,2ƒ:6ƒ,2§:6§,2¤:6¤,2¤?-sexipyridine (spy) complex

[Eu(spy)(NO3)2][NO3] lie in the range 2.536�/2.589 A

[25], with an average value of 2.569 A, whilst the Eu�/O

distances average 2.531 A. The average value for Eu�/

OH2 is 2.44 A in square-antiprismatic eight co-ordinate

[Eu(OH2)8]3� ions in [Eu(OH2)8][V10O28] �/8H2O [26],

whilst the range in the nine co-ordinate trigonal

prismatic [Eu(OH2)9]3� ions in [Eu(OH2)9][CF3SO3]3is 2.408�/2.536 A with an average of 2.451 A [27]. The

Eu�/OH2 bond length of 2.408 A in 10 co-ordinate

[Eu(terpy)(NO3)3 �/(H2O)] is shorter than either of these,

reflecting the decreased steric congestion concomitant

with the presence of bi- and tridentate ligands in the

coordination sphere of the metal.

3.3. Crystal structure of [Tb(terpy)(NO3)3 �/(H2O)]

(2)

The [Tb(terpy)(NO3)3 �/(H2O)] (2) complex (Fig. 3) is

isostructural and isomorphous with the europium ana-

logue (1), consequently the hydrogen bonding network

is very similar [O(10)� � �O(5), 3.013 A; H(10a)� � �O(5),

2.140 A, O(10)�/H(10a)� � �O(5), 163.168; with O(5)

related by the symmetry operation �/x , �/y , �/z ; and

O(10)� � �O(3), 2.970 A; H(10b)� � �O(3), 2.080 A, O(10)�/

H(10b)� � �O(3), 169.928; with O(3) related by the sym-

metry operation �/x , �/y , 1�/z ]. The graphitic packing

distance between the central ring

{N(2)C(6)C(7)C(8)C(9)C(10)} of one molecule and one

of the outer rings {N(1)C(1)C(2)C(3)C(4)C(5)} of a

molecule related by the symmetry operation 1�/x , 1�/

y , 1�/z is 3.660 A. Only the bond parameters involving

the metal centre show a significant difference between

the two complexes. Average Tb�/N and Tb�/O(nitrate)

distances are 2.549 and 2.510 A, respectively, whilst Tb�/

OH2 distance is 2.394(4) A. All of these values are

approximately 0.01 A shorter than those in the euro-

pium analogue; although ionic radii for 10 co-ordinate

Tb3� and Eu3� do not seem to be available, a

difference of approximately 0.025 A would be expected

from a comparison of the values for eight and nine co-

ordination. The Tb�/O(nitrate) and Tb�/OH2 are very

similar to the respective values of 2.56 and 2.37 A in 10

co-ordinate [Tb(H2O)4(NO3)3] �/H2O [28].

4. Conclusions

The spatial arrangement of nitrate groups in com-

plexes [Eu(L)n (NO3)3] is to an extent dictated by the

other ligands. When a tetra- or pentadentate ligand such

as a crown ether is co-ordinated to a europium centre, it

necessarily occupies one side of the co-ordination

sphere. The geometry in [Ln(bipy)2(NO3)3] closely

resembles complexes like [Eu(15-crown-5)(NO3)3] [22]

where the crown ether blocks one side of the co-

ordination sphere dictating the position adopted by

the nitrate groups. It should be noted that when the

cavity in the crown ether is sufficiently large to

accommodate a lanthanide ion in-plane, the nitrate

groups are bound on opposite sides of the plane, as in

[La(NO3)3(18-crown-6)] [29] and in the cation of

[Eu(NO3)2(18-crown-6)]3[Eu(NO3)6] [30].

Monodentate ligands necessarily offer the greatest

flexibility in accommodating the nitrate groups, but

there are subtle effects at work. In [M(H2O)4(NO3)3] �/H2O (M�/Eu, Y), one water molecule occupies a site on

the opposite side of the europium to the other three co-

ordinated water molecules [20] but in [M(H2O)4(NO3)3] �/2H2O, (M�/Nd, Pr, Tb, Y), the four co-ordinated water

molecules share a common face [31].

Since the erbium complex [Er(terpy)(NO3)3 �/(C2H5OH)] crystallises from reaction of hydrated er-

bium nitrate with terpyridyl in ethanol, we were initially

concerned that an analogous europium compound had

undergone substitution by traces of water on recrystal-

lisation from MeCN. We subsequently found that

[Tb(terpy)(NO3)3 �/(H2O)] crystallises directly from etha-

nol so that this does not appear to be the case. Since

[Eu(terpy)(NO3)3 �/(H2O)] is obtained from solution, a

complex [Eu(terpy)(NO3)3] would evidently be co-ordi-

natively unsaturated, though such species may be

isolable later in the lanthanide series, especially as the

scandium ion, smaller than the later lanthanides, forms

Fig. 3. The molecular structure of [Tb(terpy)(NO3)3 �/(H2O)] (2)

showing the atom numbering scheme adopted. Ellipsoids are set at a

value of 30%.

S.A. Cotton et al. / Inorganica Chimica Acta 344 (2003) 37�/42 41

[Sc(terpy)(NO3)3]. This has no solvent co-ordinated but

one nitrate asymmetrically co-ordinated [32], so the

coordination number of scandium is about 8.5. It is

possible that the earlier lanthanides form complexes[Ln(terpy)(NO3)3 �/(H2O)2]; we are investigating these

possibilities as part of our detailed study of the effect

of solvent and lanthanide on the composition of the

lanthanide complexes isolated across the whole lantha-

nide series.

5. Supplementary material

Crystallographic data for the structural analysis have

been deposited with the Cambridge Crystallographic

Data Centre, CCDC Nos. 184557�/184559 for com-

pounds 1, 2 and 3, respectively. Copies of this informa-

tion may be obtained free of charge from The Director,

CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK

(fax: �/44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).

Acknowledgements

We thank the EPSRC for financial support, and the

European Union for an Erasmus award (to F.L.).

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